Improving Bayesian Optimization via Training-Aware Conditional Diffusion Models
Pith reviewed 2026-06-27 18:17 UTC · model grok-4.3
The pith
Conditional diffusion models trained on Bayesian optimization tasks can approximate the distribution of the global optimum x* and support a new acquisition strategy with sub-optimality guarantees.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
We leverage Conditional Diffusion Models (CDMs) to efficiently approximate the distribution of x* and develop BO-inherent training strategies for CDMs. Motivated by the structural properties of the CDM-learned distribution, we further develop an acquisition strategy termed Diffusion-based Mode Seeking (DMS) to guide the sequential evaluation. We establish a sub-optimality guarantee for the CDM-learned distribution and demonstrate through extensive experiments that DMS outperforms standard BO baselines.
What carries the argument
Conditional Diffusion Models trained with BO-inherent strategies that approximate the distribution of the global optimum x*, from which the Diffusion-based Mode Seeking (DMS) acquisition rule extracts sequential decisions.
If this is right
- The learned distribution satisfies a sub-optimality guarantee relative to the true distribution of x*.
- DMS produces better optimization performance than standard acquisition functions on the tested problems.
- The computational cost of approximating the optimum distribution drops from repeated posterior sampling to a single trained diffusion model.
- Training strategies that embed Bayesian optimization structure into the diffusion model are sufficient to make the approximation useful for sequential decisions.
Where Pith is reading between the lines
- The same training-aware diffusion approach could be tested on acquisition functions beyond mode-seeking to see whether other information measures become tractable.
- If the sub-optimality guarantee depends on the specific training strategies, removing those strategies should measurably degrade performance on the same benchmarks.
- The method might be combined with existing Gaussian-process surrogates by using the diffusion model only for the acquisition step rather than replacing the surrogate entirely.
Load-bearing premise
The CDM produces an approximation to the distribution of x* whose mode-seeking behavior yields reliable sequential decisions without hidden bias from the generative model or training procedure.
What would settle it
An experiment on standard benchmark functions in which the DMS acquisition strategy fails to match or exceed the performance of common baselines such as expected improvement while the claimed sub-optimality bound is also violated.
Figures
read the original abstract
Bayesian optimization (BO) is a widely used approach for black-box optimization that uses a Gaussian process (GP) as a surrogate and guides sequential evaluations via an acquisition function, with the ultimate goal of locating the global optimum $\mathbf{x}^{\star}$. To align with this goal, information-based acquisition functions such as Predictive Entropy Search (PES) model $\mathbf{x}^{\star}$ as a random variable and reduce the entropy of its distribution, but approximating this distribution via traditional GP posterior sampling is computationally expensive. To address this limitation, we leverage Conditional Diffusion Models (CDMs) to efficiently approximate the distribution of $\mathbf{x}^{\star}$ and develop BO-inherent training strategies for CDMs. Motivated by the structural properties of the CDM-learned distribution, we further develop an acquisition strategy termed Diffusion-based Mode Seeking (DMS) to guide the sequential evaluation. We establish a sub-optimality guarantee for the CDM-learned distribution and demonstrate through extensive experiments that DMS outperforms standard BO baselines.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript proposes using Conditional Diffusion Models (CDMs) with custom BO-inherent training strategies to approximate the distribution of the global optimum x* in Bayesian optimization, introduces a Diffusion-based Mode Seeking (DMS) acquisition strategy based on the learned distribution's structural properties, establishes a sub-optimality guarantee for the CDM-learned distribution, and reports experimental outperformance over standard BO baselines.
Significance. If the sub-optimality guarantee is shown to apply after the BO-specific training modifications and the experiments are robust, the approach could provide a scalable alternative to expensive GP posterior sampling for information-based acquisition functions such as PES, potentially improving efficiency in high-dimensional black-box optimization.
major comments (2)
- [Abstract] Abstract: the sub-optimality guarantee is stated for the CDM-learned distribution of x*, but the training procedure uses custom BO-inherent strategies rather than standard CDM objectives. It is unclear whether these modifications preserve the conditions under which the guarantee holds (e.g., by altering the effective score-matching target), which directly affects whether DMS decisions remain reliable in sequential BO.
- [Abstract] Abstract: the claim of experimental superiority over standard BO baselines provides no detail on the specific baselines, test functions, evaluation budgets, random seeds, or whether the experimental design was fixed prior to observing results, undermining assessment of the performance claims.
Simulated Author's Rebuttal
We thank the referee for the thoughtful comments on the abstract. We address each major comment below and will make targeted revisions to improve clarity without altering the core claims.
read point-by-point responses
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Referee: [Abstract] Abstract: the sub-optimality guarantee is stated for the CDM-learned distribution of x*, but the training procedure uses custom BO-inherent strategies rather than standard CDM objectives. It is unclear whether these modifications preserve the conditions under which the guarantee holds (e.g., by altering the effective score-matching target), which directly affects whether DMS decisions remain reliable in sequential BO.
Authors: The sub-optimality guarantee is derived directly for the distribution approximated by the trained CDM (see Theorem 1 and its proof in Section 4), which depends on the learned distribution satisfying mode-concentration properties rather than on the precise training objective used to reach that distribution. Our BO-inherent training strategies modify the conditioning and loss to better align the learned distribution with the BO objective of concentrating mass near x*, but they do not change the score-matching target in a way that invalidates the concentration argument; the proof relies only on the final learned density, not the path taken during training. That said, the abstract could be clearer on this distinction, so we will revise it to read "a sub-optimality guarantee for the CDM-learned distribution after BO-aware training" and add a short clarifying sentence in Section 4. revision: yes
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Referee: [Abstract] Abstract: the claim of experimental superiority over standard BO baselines provides no detail on the specific baselines, test functions, evaluation budgets, random seeds, or whether the experimental design was fixed prior to observing results, undermining assessment of the performance claims.
Authors: We agree the abstract is terse on experimental details. The full setup (baselines: EI, UCB, PES, MES; functions: Branin, Hartmann-6, Ackley-10, etc.; budget: 50–100 evaluations; 20 random seeds; pre-registered design) appears in Section 5 and Appendix C. To address the concern we will expand the abstract sentence to "DMS outperforms standard BO baselines (EI, UCB, PES) on benchmark functions with 50 evaluations across 20 seeds." This is a minor wording change; the underlying experiments and their pre-specification remain unchanged. revision: yes
Circularity Check
No circularity: sub-optimality guarantee and DMS are independent of fitted inputs
full rationale
The abstract states a sub-optimality guarantee is established for the CDM-learned distribution of x* and that DMS is motivated by structural properties of that distribution. No equations or claims are provided that reduce this guarantee to a quantity defined by the paper's own fitted parameters, self-citations, or ansatz smuggled via prior work. The BO-inherent training strategies are described as modifications to standard CDM objectives, but without any quoted reduction showing the learned conditional equals the input by construction or that a prediction is statistically forced from a fit, the derivation chain remains self-contained against external benchmarks. This matches the most common honest finding of no significant circularity.
Axiom & Free-Parameter Ledger
axioms (2)
- domain assumption A Gaussian process surrogate adequately models the unknown black-box function for the purposes of sequential decision making
- domain assumption Conditional diffusion models can be trained to produce samples whose distribution is close enough to the true posterior over x* for acquisition purposes
invented entities (1)
-
Diffusion-based Mode Seeking (DMS) acquisition strategy
no independent evidence
Reference graph
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=N(x y t ;µ t,Σ t),with µt =x y 0 exp − 1 2 Z t 0 β(s)ds ,Σ t = 1−exp − Z t 0 β(s)ds I.(12) For notational convenience in the theoretical analysis in Appendix F and Appendix G, we equivalently denote the distribution of the transition kernel as N(x y t ;x y 0α(t), h(t)), where α(t) = exp − 1 2 R t 0 β(s)ds and h(t) = 1− exp − R t 0 β(s)ds . A.2 Classifier...
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sθ + xt h(t) − α(t)x0 h(t) 2 2 # 1{∥x 0∥2 ≤R,|y| ≤R}dt ≤ 2 T−t 0 Z T t0 Ext|x0
At the first BO iteration, all linear layers are initialized using Kaiming normal initialization with zero-initialized biases; from the second BO iteration onward, model parameters are loaded from the previous iteration. At each BO iteration, the learning rate is initialized to 1×10 −3, then we apply a warm-up phase for the first 20 epochs, during which t...
2026
discussion (0)
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